1. Field of the Invention
The present invention relates to a phase shift circuit capable of significantly reducing electromagnetic interference (EMI) in input and an output signals by controlling a phase difference between driving signals of switches operating a main circuit and a sub circuit included in a power factor correction circuit, and a power factor correction circuit including the same.
2. Description of the Related Art
Recently in the electrical engineering and electronics fields, research into a method of removing harmonic components occurring in an input terminal of an electronic device so as to significantly reduce an effect thereof on a power supply line of the electronic device and interference with other devices has been actively conducted. An efficient method of removing harmonic components may use a power factor correction circuit (PFC) which may be divided into a passive type power factor correction circuit or an active type power factor correction circuit, according to whether the power factor correction circuit includes a switch. The passive type power factor correction circuit has a large form factor and a reasonably small effect. As a result, active type power factor correction circuits are extensively used.
Among active type power factor correction circuits, an interleaved type power factor correction circuit using at least two same power factor correction circuits connected to each other in parallel has characteristics that depend on a phase difference between signals operating a plurality of circuits connected to each other in parallel. For example, in the case that two same power factor correction circuits are connected to each other in parallel in a master-slave scheme, driving signals for operating switches included in each of the two circuits have a phase difference of 180° with respect to each other, such that the electro-magnetic interference of the input and output signals may be significantly reduced. Provided the phase difference between the driving signals for each of the main circuit and the sub circuit is out of 180°, a ripple component of the input current is increased, such that the electromagnetic interference is also increased.
In the interleaved type power factor correction circuit, various types of phase shift circuits have been proposed to maintain the phase difference between the switch devices included in each circuit at a required value. However, the phase shift circuit according to the related art may have limited conditions upon selecting current sources included in the phase shift circuit or there may be a difficulty in generating a phase difference required by the phase shift circuit.
In the Related Art Document below, Patent Document 1 relates to an interleaved type switching converter, a control apparatus, and a method thereof and discloses a method of generating a control signal by switching a power supply using an interleaved type and keeping a phase difference of a required value, 180°. Patent Document 2 relates to a phase shift and synchronous circuit and discloses contents regarding control of sinking between control signals of each switch device in an interleaved type power factor correction circuit. However, both of Patent Documents 1 and 2 do not disclose a configuration of offsetting an overall average of offset components by changing a negative or positive value of the offset components of an input signal every period in the phase shift circuit only including a single current source.